De‑O‑acylated lipooligosaccharide of E.�coli B reduces the number of metastatic foci via downregulation of myeloid cell activity

Lipopolysaccharides are the main surface antigens and virulence factors of gram‑negative bacteria. Removal of four ester‑bound fatty acid residues from hexaacyl lipid A of Escherichia coli lipooligosaccharide (LOS) resulted in the de‑O‑acylated derivative E. coli LOS‑OH (LOS‑OH). This procedure caused a significant reduction in the toxicity of this compound compared to the native molecule. We investigated the effect of such a structural LOS modification on its biological activity using in vitro assays with monocytic cells of the RAW264.7 line, dendritic cells of the JAWS II line, bone marrow‑derived dendritic cells (BM‑DCs), and spleen cells. Furthermore, in in vivo experiments with a melanoma B16 metastasis model, the anti‑metastatic activity of the compounds and spleen cell reactivity mediated by them representing a systemic response were analyzed. The results revealed that LOS‑OH demonstrated weaker ability than LOS to stimulate and polarize an immune response both in vitro and in vivo. It induced lower cytokine production by cells of myeloid lines. Multiple applications of LOS‑OH into mice injected intravenously with B16 cells significantly (P